The present invention is related to a vacuum-operated brake power booster with a movable wall sealed off relative to the vacuum housing. A piston rod coupled with a brake pedal serves to actuate a control valve by means of which a power chamber of the brake power booster is connectible at option either to vacuum or to a more elevated differential pressure. The control valve is furnished with a control valve piston adapted to slide axially within a control valve body. The control valve piston acts on one end of a push-rod to slide the piston of a master cylinder, with a reaction element interposed between the control valve piston and the push-rod.
There is a desire to reduce the weight and overall length of modern power brake units. However, accomplishing these two goals usually involves facing the following diadvantages: the lower weight materials such as aluminum utilized for the booster provide a poorer degree of silencing of the suction noise of the power brake unit, and due to the reduced overall length, the ventilation ducts for the power chamber are located deep within the cylindrical neck portion of the vacuum housing. The air flows at high velocity against vibrations are irradiated over the whole surface of the housing, thereby causing an annoying suction noise.
The present invention has an object to provide a vacuum-operated brake power booster having a decreased development of noise by the booster during brake operation.